I've mentioned the three types of spell components in Dungeons & Dragons (and many other games) before. Material components are the physical items you need to cast a spell; somatic components are the gestures you need to make; and verbal components are the magical incantations you need to speak.

Many game spells specify material components, which might include various pinches of appropriate herbs or chemicals, but can also include valuable objects which serve to limit how often the spells can be cast, by giving them an economic cost. But very few games specify the verbal components of spells - the actual magical words that the spellcaster needs to say.

You could try writing some suitable incantations and enforcing that the player playing a spellcaster needs to recite the words to cast the spell in-game. It could be annoying, but I could also see it as a way of getting more deeply into character. Instead of a player saying, "I'm going to cast a fireball", they could simply start reciting the spell, and the GameMaster could respond appropriately.